Field effect transistor, integrated circuit element, and method for manufacturing the same

ABSTRACT

A field effect transistor of an embodiment of the present invention includes, a semiconductor substrate containing Si atoms; a protruding structure formed on the semiconductor substrate; a channel region formed in the protruding structure and containing Ge atoms; an under channel region formed under the channel region in the protruding structure and containing Si and Ge atoms, the Ge composition ratio among Si and Ge atoms contained in the under channel region continuously changing from the channel region side to the semiconductor substrate side; a gate insulating film formed on the channel region; and a gate electrode formed on the gate insulating film on the channel region.

CROSS REFERENCE TO RELATED APPLICATION

This application is based upon and claims the benefit of priority fromprior Japanese Patent Application No. 2006-182448, filed on Jun. 30,2006, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a field effect transistor, anintegrated circuit element, and a method for manufacturing the same.

2. Background Art

Increasing a drive current per unit gate length of each MOSFET, byreducing the gate length and thinning the gate insulating film, is aconventional general approach to enhance the performance andfunctionality of a CMOS circuit element. Thereby, the size of a MOSFETto provide a required drive current is reduced, which allows higherintegration of MOSFETs, and a drive voltage to provide a required drivecurrent is decreased, which reduces power consumption per unit element.

However, in recent years, technical difficulty to achieve a requiredhigh performance and functionality, by reducing the gate length andthinning the gate insulating film, has been rapidly increasing. Use ofhigh-mobility channel material is effective to alleviate this situation.For example, strain-free SiGe (silicon germanium) and Ge (germanium) areeffectively used for both of pMOS and nMOS, since these materials havehigher electron mobility and hole mobility than Si (silicon). Further,compressive-strained Si, SiGe and Ge are effectively used for pMOS,since these materials have high hole mobility. Further, tensile-strainedSi, SiGe and Ge are effectively used for nMOS, since these materialshave high electron mobility.

Furthermore, it is possible, by using a structure having a plurality ofgates, to increase the drive current while maintaining a sufficientlylow off-state current. Examples of the structure include, a double-gatestructure in which a gate electrode and a gate insulating film areformed on both sides of a channel, a tri-gate structure in which a gateelectrode and a gate insulating film are formed on three sides (rightside, left side, and upper side) of a channel, and a gate-all-around(GAA) structure in which a channel is surrounded by a gate electrode anda gate insulating film. These structures are called multi-gatestructures (three-dimensional gate structures). Electrostatic forceprovided by their gates to control channel carriers, is larger than thatprovided by a typical single gate structure (planar gate structure).Therefore, in these multi-gate structures, the short channel effect canbe suppressed even when the channel impurity concentration is low. Inparticular, an FET manufactured by, forming a plate-like protrusion(fin) on a substrate, forming a channel in the protrusion, and forming agate electrode and a gate insulating film on both sides of the channel,is called FinFET.

Use of the high-mobility channel material and any of the multi-gatestructures in combination, provides higher performance and functionalitycompared to using each technology alone. In fact, various kinds ofpreceding art using these technologies in combination, are disclosed invarious preceding documents.

The preceding art can be broadly classified into three types oftechnologies.

The first preceding art relates to an FET formed on an SOI(Semiconductor-On-Insulator) substrate. For example, JP-A 2003-243667(KOKAI) discloses a strained Si-FinFET manufactured by, forming a finmade of SiGe on an embedded insulating film of an SGOI(SiGe-On-Insulator) substrate, and forming strained Si around the fin.Further, JP-A 2005-159362 (KOKAI) discloses a strained Ge-FinFETmanufactured by, forming a fin made of Si on an embedded insulating filmof an SOI (Si-On-Insulator) substrate, and forming strained Ge aroundthe fin. In each of these FETs, a strained layer that receives strain isformed on a core layer that induces strain, and a hetero-interface ispresent between the core layer and the strained layer.

The second preceding art relates to an FET formed on a bulk substrate.For example, JP-A 2005-203798 (KOKAI) discloses a multi-gate transistormanufactured by, forming a Ge layer in a predetermined region on a Sisubstrate by vapor epitaxial deposition, and forming a gate structurethat uses the resultant facet as the channel. Further, JP-A 2005-79517(KOKAI) discloses a multichannel-type double-gate transistormanufactured by, forming an amorphous SiGe layer in the lateraldirection from the source/drain region in a Si layer by solid epitaxialdeposition. In the former case, the Ge layer is formed on the Sisubstrate, and a hetero-interface is present between the Si substrateand the Ge layer. In the latter case, the SiGe layer is formed on the Silayer, and a hetero-interface is present between the Si layer and theSiGe layer.

The third preceding art relates to a basic technology assumed to beapplied to an FET. “Tsung-Yang Liow et al., Applied Physics Letters Vol.87, p 262104 (2005)” discloses a method for forming a high Gecomposition SiGe-Fin structure on a lattice-relaxed SiGe substrate. Morespecifically, the document discloses a method such as, forming alattice-relaxed SiGe layer having a thickness of about a few μm on a Sisubstrate, processing the SiGe layer into a fin-like shape, andperforming thermal oxidization of the Si substrate, to thin the fin andincrease Ge composition in the fin.

However, these kinds of preceding art have some disadvantages.

In the first and second preceding art, a hetero-interface in which Geconcentration abruptly changes across the interface, such as thehetero-interface between the Si layer and the SiGe layer and thehetero-interface between the Si layer and the Ge layer, is formed duringthe epitaxial deposition. Therefore, in the first and second precedingart, there is a strong possibility that lattice defects occur in achannel region or the like. The lattice defects in the channel region orthe like cause problems, such as increased leak current in thetransistor and reduced reliability of the transistor. In the thirdpreceding art, oxidation-induced condensation at a low temperature of875° C. causes insufficient interdiffusion of Si and Ge atoms, whichalso causes abrupt gradient of Ge concentration and the occurrence oflattice defects. Further, in “Tsung-Yang Liow et al., Applied PhysicsLetters Vol. 87, p 262104 (2005)” corresponding to the third art, thesubstrate including the Si substrate and the lattice-relaxed SiGe layer,is employed as a substrate. Since the cost for forming the thick SiGelayer by the epitaxial deposition is very high, the price of thissubstrate is a couple to decades of times higher than that of a typicalbulk substrate. Therefore, if such a substrate is employed tomanufacture transistors, the cost of the entire integrated circuitelement increases greatly. In addition, the heat conductivity of SiGe islower than that of Si by a couple of orders. Therefore, in a transistormanufactured by using such a substrate, Joule heat generated when acurrent passes through a channel is not dissipated sufficiently, whichincreases the channel temperature. As a result, characteristics of thetransistor are degraded.

SUMMARY OF THE INVENTION

An embodiment of the present invention is, for example, a field effecttransistor including:

a semiconductor substrate containing Si atoms;

a protruding structure formed on the semiconductor substrate;

a channel region formed in the protruding structure and containing Geatoms;

an under channel region formed under the channel region in theprotruding structure and containing Si and Ge atoms, the Ge compositionratio among Si and Ge atoms contained in the under channel regioncontinuously changing from the channel region side to the semiconductorsubstrate side;

a gate insulating film formed on the channel region; and

a gate electrode formed on the gate insulating film on the channelregion.

Another embodiment of the present invention is, for example, a fieldeffect transistor including:

a semiconductor substrate containing Si atoms;

a protruding structure formed on the semiconductor substrate;

a channel region formed in the protruding structure and containing Geatoms;

an insulating film embedded under the channel region;

a gate insulating film formed on the channel region; and

a gate electrode formed on the gate insulating film on the channelregion.

Another embodiment of the present invention is, for example, a methodfor manufacturing a field effect transistor, the method including:

forming a protruding structure on a semiconductor substrate containingSi atoms;

by thermal oxidization, forming a channel region containing Ge atoms inthe protruding structure;

by changing the temperature of the thermal oxidization from a hightemperature to a low temperature, forming an under channel regioncontaining Si and Ge atoms under the channel region in the protrudingstructure, the Ge composition ratio among Si and Ge atoms contained inthe under channel region continuously changing from the channel regionside to the semiconductor substrate side;

forming a gate insulating film on the channel region; and

forming a gate electrode on the gate insulating film on the channelregion.

Another embodiment of the present invention is, for example, a methodfor manufacturing a field effect transistor, the method including:

forming a protruding structure on a semiconductor substrate containingSi atoms;

by thermal oxidization under the condition that a mask covers the areaaround the region where a channel region is to be formed, forming achannel region containing Ge atoms in the protruding structure;

by changing the temperature of the thermal oxidization from a hightemperature to a low temperature, forming an under channel regioncontaining Si and Ge atoms under the channel region in the protrudingstructure, the Ge composition ratio among Si and Ge atoms contained inthe under channel region continuously changing from the channel regionside to the semiconductor substrate side, and forming channel sideregions containing Si and Ge atoms at sides of the channel region, theGe composition ratio among Si and Ge atoms contained in the channel sideregions continuously changing from the channel region sides tosource/drain region sides;

forming source/drain regions containing Si and Ge atoms at sides of thechannel region, the Ge composition ratio among Si and Ge atoms containedin the source/drain regions being lower than the Ge composition ratio inthe channel region;

forming a gate insulating film on the channel region; and

forming a gate electrode on the gate insulating film on the channelregion.

Another embodiment of the present invention is, for example, a methodfor manufacturing a field effect transistor, the method including:

forming a protruding structure on a semiconductor substrate containingSi atoms;

forming a cavity in the protruding structure;

embedding an insulating film in the cavity;

by thermal oxidization, forming a channel region containing Ge atoms inthe protruding structure;

forming a gate insulating film on the channel region; and

forming a gate electrode on the gate insulating film on the channelregion.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanatory view showing a transistor of the firstembodiment;

FIGS. 2A to 2I are explanatory views showing a method for manufacturingthe transistor of the first embodiment;

FIG. 3 is an explanatory view showing a transistor of the secondembodiment;

FIGS. 4A to 4I are explanatory views showing a method for manufacturingthe transistor of the second embodiment;

FIG. 5 is an explanatory view showing a transistor of the thirdembodiment;

FIGS. 6A to 6G are explanatory views showing a method for manufacturingthe transistor of the third embodiment;

FIG. 7 is an explanatory view showing a transistor of the fourthembodiment;

FIG. 8 is an explanatory view showing a method for manufacturing thetransistor of the fourth embodiment;

FIG. 9 is an explanatory view showing a transistor of the fifthembodiment;

FIG. 10 is an explanatory view showing a method for manufacturing thetransistor of the fifth embodiment;

FIG. 11 is an explanatory view showing a transistor of the sixthembodiment;

FIGS. 12A to 12C are explanatory views showing a method formanufacturing the transistor of the sixth embodiment;

FIG. 13 is an explanatory view showing a transistor of the seventhembodiment;

FIG. 14 is an explanatory view showing a transistor of the eighthembodiment;

FIG. 15 is an explanatory view showing a CMOS circuit of the ninthembodiment; and

FIG. 16 shows the relationship between the composition gradient and thethreading dislocation density in a Si_(1-x)Ge_(x) region.

DESCRIPTION OF THE EMBODIMENTS First Embodiment

FIG. 1 is an explanatory view showing a field effect transistor 101 ofthe first embodiment. FIG. 1 shows, the top view of the field effecttransistor 101, the side cross-sectional view showing the cross sectionX of the field effect transistor 101, and the side cross-sectional viewshowing the cross section Y of the field effect transistor 101. Thefield effect transistor (FET) 101 shown in FIG. 1 is a MOSFET, which maybe a P-MOSFET or an N-MOSFET.

The field effect transistor 101 shown in FIG. 1 includes a Si substrate111 which is a specific example of a semiconductor substrate, a finstructure 112 which is a specific example of a protruding structure, agate insulating film 113, a gate electrode 114, side wall insulatingfilms 115, source/drain electrodes 116, and the like. In the finstructure 112 shown in FIG. 1, there are formed a channel region 121, anunder channel region 122, source/drain regions 131, under source/drainregions 132, over source/drain regions 133, extension regions 141, andthe like.

The field effect transistor 101 employs a multi-gate structure, so gatesare formed on a plurality of “channel surfaces” of the channel region121 (which mean “exposed sides” of the channel region 121 exposed to thesurface of the fin structure 112). Particularly in this embodiment, thefield effect transistor 101 employs a tri-gate structure, so gates areformed on the following three channel surfaces of the channel region121: a first lateral channel surface S1, a second lateral channelsurface S2, and an upper channel surface S3. The channel surfaces S1 andS2 which are perpendicular to the principal plane of the Si substrate111, and the channel surface S3 which is parallel to the principal planeof the Si substrate 111, are used as surfaces to form gates thereon. Inthe field effect transistor 101, the gate insulating film 113 is formedon the channel region 121 (in detail, on the plurality of channelsurfaces of the channel region 121: S1, S2, and S3). In the field effecttransistor 101, the gate electrode 114 is formed on the gate insulatingfilm 113 on the channel region 121 (in detail, on the plurality ofchannel surfaces of the channel region 121: S1, S2, and S3).

In the field effect transistor 101, the fin structure 112 is formed onthe Si substrate 111. The Si substrate 111 is a semiconductor substratemade of Si atoms and corresponds to a bulk Si substrate. The finstructure 112 is a fin-shaped protruding structure and made of asemiconductor layer containing Si and Ge atoms. The substrate 111 maycontain only Si atoms, or may contain Si atoms and other atoms. The finstructure 112 may contain only Si and Ge atoms, or may contain Si and Geatoms and other atoms.

In the fin structure 112, the source/drain regions 131 and the extensionregions 141 are formed at sides of the channel region 121. Thesource/drain regions 131 and the extension regions 141 are provided onboth sides of the channel region 121 such that the channel region 121 issandwiched by the source/drain regions 131 and the extension regions141. The fin structure 112 contains Si atoms and Ge atoms, and the ratioof the Si atoms to the Ge atoms contained therein varies depending onlocations. The channel region 121, the source/drain regions 131, and theextension regions 141 are Ge regions made of Ge atoms or Si_(1-x)Ge_(x)regions made of Si and Ge atoms, where “x” represents the Ge compositionratio among contained Si and Ge atoms and is calculated by the followingequation: (molar concentration of Ge atoms)/(molar concentration of Siatoms+molar concentration of Ge atoms). FIG. 1 also shows a profile ofthe Ge composition ratio “x” on the horizontal line L1 connecting thechannel region 121, the source/drain regions 131, and the extensionregions 141. The channel region 121, the source/drain regions 131, andthe extension regions 141 may contain only Ge atoms, or may contain Geatoms and other atoms. The channel region 121, the source/drain regions131, and the extension regions 141 may contain only Si and Ge atoms, ormay contain Si and Ge atoms and other atoms.

Furthermore, under the channel region 121, there is a region where theGe composition ratio “x” continuously changes from the channel region121 side to the Si substrate 111 side (the under channel region 122).This region extends to regions under the source/drain regions 131 (theunder source/drain regions 132). FIG. 1 also shows a profile of the Gecomposition ratio “x” on the vertical line L2 connecting the channelregion 121 and the under channel region 122. The under channel region122 and the under source/drain regions 132 may contain only Si and Geatoms, or may contain Si and Ge atoms and other atoms.

Furthermore, over the source/drain regions 131, there are regions madeof Ni (nickel) suicide (the over source/drain regions 133). Each of theregions in the fin structure 112 will be described below in more detail.

As apparent from the profile shown in FIG. 1, the channel region 121,the source/drain regions 131, and the extension regions 141 in thisembodiment are Ge regions, in which the Ge composition ratio “x” is100%. These regions may be Si_(1-x)Ge_(x) regions having a Gecomposition ratio “x” of 80% or higher. Comparing the mobility in thechannel region 121 made of Si and the mobility in the channel region 121made of Si_(1-x)Ge_(x), in the case of pMOS, the latter is higher at anarbitrary Ge composition ratio “x”, while in the case of nMOS, thelatter is higher only when the Ge composition ratio “x” is higher than80%. Therefore, the Ge composition ratio “x” of 80% or higher in thechannel region 121 and the like provides an advantage that the Gecomposition ratio “x” in the channel region 121 and the like can be thecommon value for a pMOS and an nMOS.

The distance from the upper side of the fin structure 112 (the interfacewith the gate insulating film 113) to the lower side of the finstructure 112 (the interface with the Si substrate 111), that is, theheight of the fin structure 112 “h1”, is 200 nm in this embodiment. Theheight of the channel region 121 surrounded by the gate insulating film113 and the gate electrode 114, “h2”, is 100 nm in this embodiment. Asdescribed above, under the channel region 121, source/drain regions 131,and extension regions 141, the Ge composition ratio “x” continuouslychanges (decreases) in the vertical direction from the channel region121 side to the Si substrate 111 side, such that the Ge compositionratio “x” decreases to as low as about 1% at the height substantiallysame as the upper side of the Si substrate 111. The shorter is the “d”:the distance from the height of the lower end of the gates surroundingthe fin structure 112 (i.e. the lower end of the channel region 121) tothe height where the Ge composition ratio “x” becomes 1%, the closer arethe channel region 121 and the Si substrate 111 whose heat conductivityis high, resulting in good heat dissipation from the channel region 121.The present inventor performed a simulation and found that the distance“d” of 250 nm or shorter could suppress the temperature increase in thechannel region 121 to 30 K or lower. In this embodiment, since thedistance “d” is 100 nm (=h1−h2=200 [nm]−100 [nm]) which is very short,the heat dissipation from the channel region 121 is excellent. Since thedistance “d” is the amount corresponding to the thickness of the portionwhere the under channel region 122 is present, the distance “d” ishereinafter referred to as the thickness of the under channel region 122(from the channel region 121 side to the Si substrate 111 side). The finwidth “t” is 10 nm in this embodiment. The gate length “l” is 20 nm inthis embodiment.

Furthermore, under the channel region 121, source/drain regions 131, andextension regions 141, the gradient of the profile in FIG. 1, i.e., therate of change of the Ge composition ratio “x” from the channel region121 side to the Si substrate 111 side, “r”, is 5%/nm or lower. Thecomposition gradient “r” and the occurrence of lattice defects have thefollowing close correlation, so that the composition gradient “r” in theunder channel region 122 and the like is set to 5%/nm or lower in thisembodiment. The graph in FIG. 16 shows the relationship between thecomposition gradient “r” and the threading dislocation density “n” in aSi_(1-x)Ge_(x) region. In the graph in FIG. 16, there is plotted themeasurement result obtained by, forming a gradient composition layer ofSi_(1-x)Ge_(x) having a thickness of d [nm] and a uniform compositionlayer of Si_(0.5)Ge_(0.5) having a thickness of 20 [nm] on a Sisubstrate by epitaxial deposition, annealing the wafer formed of thesethree layers at 800° C. for 30 minutes, and measuring the threadingdislocation density “n” in the gradient composition layer. Thecomposition gradient “r” [%/nm] in the gradient composition layer iscalculated by 50 [%]/d [nm]. According to the measurement resultobtained by the present inventor, it has been found that when thecomposition gradient “r” exceeds 5%/nm, the threading dislocationdensity “n” abruptly increases. In this embodiment, the under channelregion 122 and the like having gradient composition are provided underthe channel region 121 and the like, which reduces the possibility ofthe occurrence of lattice defects in the channel region 121 and thelike, and the composition gradient in the under channel region 122 andthe like is set to 5%/nm or lower, which further reduces the possibilityof the occurrence of lattice defects in the channel region 121, underchannel region 122, and the like.

To achieve both the effect of dissipating heat from the channel region121 and the effect of reducing the possibility of the occurrence oflattice defects in the channel region 121 and the like, the distance “d”is preferably within the range, for example, from 20 nm to 250 nm.However, since the distance “d” is set appropriately according to thefin width “t”, the distance “d” is not limited to the above range.

In this embodiment, since it is not necessary to employ an SOI substrateas the substrate and a bulk substrate can be employed as the substrate,an inexpensive bulk substrate is employed instead of an expensive SOIsubstrate. This reduces the cost of the entire integrated circuitelement in this embodiment.

In this embodiment, a P-MOSFET and an N-MOSFET which form a CMOScircuit, are constituted by the fundamental structures described above.In the pMOS, boron is doped into the source/drain regions 131 and theextension regions 141, while arsenic is doped into the channel region121, under channel region 122, under source/drain regions 132, and thelike. In the nMOS, antimony is doped into the source/drain regions 131and the extension regions 141, while boron is doped into the channelregion 121, under channel region 122, under source/drain regions 132,and the like. The over source/drain regions 133 and the gate electrode114 are made of Ni silicide in this embodiment. The gate insulating film113 is a HfSiON film having a thickness of 2.5 nm in this embodiment.

In the channel region 121, the stress resulting from the difference oflattice constants between Si and Ge is relaxed when the horizontaldirection (Y direction) and the vertical direction (Z direction), whichare perpendicular to the current direction, become open endssubstantially, but uniaxial compressive stress remains in the currentdirection (X direction). Therefore, in the channel region 121, there is0.5% compressive strain in the current direction (X direction). As aresult, the hole mobility in the channel region 121 is about five timesthe hole mobility of Si, while the electron mobility in the channelregion 121 is about twice the electron mobility of Si. The strain in thechannel region 121 decreases as the fin height “h1” increases, while thestrain increases as the fin height “h1” decreases. The uniaxialcompressive stress in this embodiment is effective to improve the holemobility, but it reduces the electron mobility. Examples of effectiveapproaches to increase the drive force of the nMOS include, increasingthe fin height “h1” (e.g. 500 nm) to decrease the compressive stress,using a Si nitride film having internal tensile stress as the side wallinsulating films 115 to cancel the compressive stress, applying tensilestress in the opposite direction of the compressive stress, and thelike. Other examples of effective approaches include, increasing thethickness of the SiGe layer in the extension, decreasing the average Gecomposition, and the like. On the other hand, examples of effectiveapproaches to increase the drive force of the pMOS include, decreasingthe fin height “h1” (e.g. 100 nm) to increase the compressive stress,using a Si nitride film having internal compressive stress as the sidewall insulating films 115 to further increase the compressive stress,and the like.

FIGS. 2A to 2I are explanatory views showing a method for manufacturingthe field effect transistor 101 of the first embodiment. FIGS. 2A to 2Ishow, top views concerning the field effect transistor 101 to bemanufactured, and side cross-sectional views showing the cross section X(see FIG. 1) concerning the field effect transistor 101 to bemanufactured.

Firstly, a strained Si_(0.85)Ge_(0.15) layer 112A having a thickness of120 nm, is formed on a Si substrate 111 by epitaxial deposition as alayer forming a fin structure 112, and a Si cap layer 112B having athickness of 10 nm, is formed on the SiGe layer 112A by epitaxialdeposition as a layer forming the fin structure 112. Then, a Si thermaloxide film 201 having a thickness of 4 nm is formed on the Si layer112B, and a Si nitride film 202 is formed on the Si thermal oxide film201 by CVD. Then, the Si nitride film 202 is patterned into a squareshape by photolithography, and then, the Si layer 112B, the SiGe layer112A, and the Si substrate 111 are etched to the depth of 150 nm by RIE.Thereby, the fin structure 112 is formed on the Si substrate 111 (FIG.2A).

Next, the fin structure 112 is thinned and the Ge composition ratio inthe fin structure 112 is increased, by thermal oxidization of the finstructure 112 (oxidation-induced condensation). The width of the finafter the thermal oxidization is 10 nm, and the Ge composition ratio inthe fin structure 112 after the thermal oxidization is substantially100% (FIG. 2B). During the thermal oxidization, the temperature of thethermal oxidization is changed (decreased) stepwise or continuouslyaccording to the change (increase) of Ge composition ratio. By suchtemperature adjustment, an under channel region 122 and the like havinga composition gradient are formed under a channel region 121 and thelike, and by controlling the rate of temperature change of the thermaloxidization temperature appropriately, the Ge atoms can be diffusedappropriately to achieve a composition gradient of 5%/nm or lower in theunder channel region 122 and the like. In this embodiment, during thethermal oxidization, the temperature of the thermal oxidization isdecreased stepwise to 1150° C., 1050° C., 1000° C., and 870° C.according to the increase of the Ge composition ratio. Since the meltingpoint of the Si_(1-x)Ge_(x) layer 112A (x≧0.8) decreases with theincrease in the Ge composition ratio “x”, it is necessary to control thetemperature of the thermal oxidization to be always lower than themelting point of the Si_(1-x)Ge_(x) layer 112A, which decreases duringthermal oxidization.

Next, the Si nitride film 202 is slimmed by CDE or wet etching with hotphosphoric acid. Then, a Si oxide film 203 is deposited by CVD, so thatthe region around the fin structure 112 is filled with the Si oxide film203. Then, the Si oxide film 203 is planarized by CMP until the surfaceof the Si nitride film 202 is exposed. Then, channel ions andpunch-through stopper ions (boron for nMOS and arsenic for pMOS) areimplanted into the channel region 121, under channel region 122, and thelike (FIG. 2C).

Next, the Si oxide film 203 is etched to the depth of 100 nm by RIEusing the Si nitride film 202 as a mask. Then, the Si nitride film 202,and the residual Si oxide film 203 on the sides of the fin structure112, are removed by wet etching with hot phosphoric acid and wet etchingwith diluted hydrofluoric acid. Thereby, a plurality of channel surfacesof the channel region 121 are exposed above the substrate (FIG. 2D).

Next, a HfSiON film 113 having a thickness of 2.5 nm which is to be agate insulating film 113, is deposited over the entire surface by CVD.Then, a poly Si layer 114 which is to be a gate electrode 114, isdeposited over the entire surface (FIG. 2E).

Next, gate processing is performed by photolithography and RIE. Then, aSi oxide film 115A and a Si nitride film 115B which is to be side wallinsulating films 115 (first side wall insulating films) are deposited,and gate side wall processing is performed by RIE (FIG. 2F).

Next, a SiGe cap 211 is formed on the exposed surface of the finstructure 112 by epitaxial deposition. Then, impurity ions (antimony fornMOS and boron for pMOS) are implanted into the fin structure 112 toform the raised extension region 141 in the fin structure 112. Theimpurities are implanted into the fin structure 112 from the obliquedirection, and they are also implanted into side wall insulating films115. The Ge composition ratio in the SiGe cap 211 is gradually decreasedfrom the lower side (the interface with the fin structure) to the upperside in order to suppress the occurrence of dislocation, such that thetop surface of the SiGe cap 211 is made of only Si (i.e. x=0). It is notnecessary that the Ge composition in the cap change continuously, andthe Ge composition in the cap may be uniform composition (e.g., x=0.4)or stepwise composition (e.g., a film of x=0 is laminated on a film ofx=0.4). In this case, however, the thickness of each of the layers ispreferably smaller than the critical film thickness within whichdislocation may not occur. A specific value of the critical filmthickness is described, for example, in “D. C. Houghton, Journal ofApplied Physics, vol. 70, p. 2136 (1991).” Then, the impurities areactivated by RTA (FIG. 2G).

Next, a Si oxide film 115C which is to be side wall insulating films 115(second side wall insulating films) is deposited by CVD, and gate sidewall processing is performed by RIE. Then, impurity ions (antimony fornMOS and boron for pMOS) are implanted into source/drain regions 131 anda poly Si layer 114 (gate electrode 114) (FIG. 2H).

Next, the upper sides of the source/drain regions 131 and the entirepoly Si layer 114 (gate electrode 114) are Ni-silicided. Then, the gatestructure is covered with an interlayer insulating film 221. Then,contact holes are formed in the interlayer insulating film 221. Then,source/drain electrodes 116 are formed in the contact holes. Thereby,the field effect transistor 101 shown in FIG. 1 is completed (FIG. 2I).

In this embodiment, although the upper side of the fin structure 112 isused as a channel, it is not necessary that the upper side of the finstructure 112 be used as a channel. When the upper side is not used as achannel, the process of removing the Si nitride film 202 (FIG. 2D) isnot required.

According to the transistor structure of this embodiment, the highmobility resulting from strain-free Ge or strained Ge provides a drivecurrent larger than that achieved in a conventional Si-FinFET. Further,since there is no abrupt change of Ge composition (hetero-interface)between the channel region 121 and the Si substrate 111, crystal defectswill not likely occur in the channel region 121 and the like. Further,since the fin structure 112 is formed on the bulk Si substrate 111, thecost is reduced compared to the case where the fin structure 112 isformed on an SOI substrate or a lattice-relaxed SiGe substrate. Further,since the heat dissipation efficiency from the channel region 121 to theSi substrate 111 is excellent and hence the channel temperature can bemaintained at low temperatures, a larger drive current is obtained. Inaddition, there is also an advantage such that transistors of thisembodiment can be combined easily with a bulk CMOS-based analog circuitand/or interface circuit to achieve SoC (System-on-Chip).

Further, according to the transistor manufacturing method of thisembodiment, compared to the case where a high concentration SiGe layer(or Ge layer) is formed directly on a Si substrate by epitaxialdeposition, the occurrence of lattice defects is reduced and hence theyield is improved; this is because the stress is released from the edgesof the fin structure 112 and the hetero-interface is eliminated by theGe diffusion during the high temperature oxidation (oxidation-inducedcondensation).

Second Embodiment

FIG. 3 is an explanatory view showing a field effect transistor 101 ofthe second embodiment. With regard to the field effect transistor 101 ofthe second embodiment, description of the things common to the firstembodiment will be omitted (the following embodiments will be treatedsimilarly).

In this embodiment, the channel region 121 and the source/drain regions131 are a Ge region and Si_(1-x)Ge_(x) regions respectively, so the Gecomposition ratio “x” in the source/drain regions 131 is lower than theGe composition ratio “x” in the channel region 121. In the case that theGe composition ratio in the source/drain regions 131 is lower than theGe composition ratio in the channel region 121 like this embodiment, theband gaps in the source/drain regions 131 become larger, so that the pnjunction leakages in the source/drain regions 131 will be reduced.

Furthermore, in this embodiment, as apparent from the top view of FIG.3, the width of the source/drain regions 131 in the Y direction islarger than the width of the channel region 121 in the Y direction.Therefore, the parasitic resistance in the FET 101 of the secondembodiment is smaller than that in the FET 101 of the first embodiment.

Furthermore, in this embodiment, at sides of the channel region 121,there are regions, between the channel region 121 and the source/drainregions 131, where the Ge composition ratio continuously changes fromthe channel region 121 sides to the source/drain region 131 sides(channel side regions 123). FIG. 3 also shows a profile of the Gecomposition ratio “x” on the horizontal line L1 connecting the channelregion 121, the channel side regions 123, and the source/drain regions131. As shown in the profile, at the sides of the channel region 121,the Ge composition ratio “x” continuously changes (decreases) in thehorizontal direction from the channel region 121 sides to thesource/drain region 131 sides. In this embodiment, the channel sideregions 123 having gradient composition is provided at sides of thechannel region 121, which reduces the possibility of the occurrence oflattice defects in the channel region 121 and the like. The channel sideregions 123 may contain only Si and Ge atoms, or may contain Si and Geatoms and other atoms.

FIGS. 4A to 4I are explanatory views showing a method for manufacturingthe field effect transistor 101 of the second embodiment. With regard tothe method for manufacturing the field effect transistor 101 of thesecond embodiment, description of the things common to the firstembodiment will be omitted (the following embodiments will be treatedsimilarly).

Firstly, as in FIG. 2A, the fin structure 112 is formed on the Sisubstrate 111. Then, a Si oxide film 301 is deposited over the entiresurface by CVD, and then, a Si nitride film 302 is deposited over theentire surface by CVD. Then, a window 311 is formed in the Si oxide film301 and the Si nitride film 302 by photolithography and RIE. The window311 is formed in the region where the channel region 121 is to beformed. Thereby, the area around the region where the channel region 121is to be formed (e.g. the region where the source/drain regions 131 areto be formed), is covered with a mask formed of the Si oxide film 301and the Si nitride film 302 (FIG. 4A).

Next, as in FIG. 2B, thermal oxidization of the fin structure 112 isperformed. In this embodiment, the mask covers the area around theregion where the channel region 121 is to be formed, so generally, bythe thermal oxidization, the Ge composition ratio in the channel region121 is increased, while the Ge composition ratio in the area around thechannel region 121 is not increased (FIG. 4B). During the thermaloxidization, the temperature of the thermal oxidization is decreasedstepwise or continuously from a high temperature to a low temperature,for example, from 1150° C. to 870° C., according to the increase of Gecomposition ratio. By such temperature adjustment, the interdiffusion ofthe Si and Ge atoms is accelerated, and hence the under channel region122 having composition gradient of 5%/nm or lower is formed under thechannel region 121, and the channel side regions 123 having compositiongradient of 5%/nm or lower are formed at sides of the channel region121. Thereby, the occurrence of lattice defects in the channel region121, under channel region 122, channel side regions 123, and the like,can be suppressed.

Next, the Si oxide film 301 and the Si nitride film 302 are removed byhot phosphoric acid wet etching. Then, as in FIG. 2C, a Si oxide film203 is deposited by CVD, so that the region around the fin structure 112is filled with the Si oxide film 203. Then, the Si oxide film 203 isplanarized by CMP until the surface of the Si nitride film 202 isexposed. Then, channel ions and punch-through stopper ions (boron fornMOS and arsenic for pMOS) are implanted into the channel region 121,under channel region 122, and the like (FIG. 4C).

Next, as in FIG. 2D, the Si oxide film 203 is etched to the depth of 100nm by RIE using the Si nitride film 202 as a mask. Then, the Si nitridefilm 202, and the residual Si oxide film 203 on the sides of the finstructure 112, are removed by wet etching with hot phosphoric acid andwet etching with diluted hydrofluoric acid. Thereby, a plurality ofchannel surfaces of the channel region 121 are exposed above thesubstrate (FIG. 4D).

Next, as in FIG. 2E, a HfSiON film 113 which is to be a gate insulatingfilm 113, is deposited by CVD Then, a poly Si layer 114 which is to be agate electrode 114, is deposited (FIG. 4E).

Next, as in FIG. 2F, gate processing is performed by photolithographyand RIE. Then, a Si oxide film 115A and a Si nitride film 115B which isto be side wall insulating films 115 (first side wall insulating films)are deposited, and gate side wall processing is performed by RIE (FIG.4F).

Next, as in FIG. 2G, a SiGe cap 211 is formed on the exposed surface ofthe fin structure 112 by epitaxial deposition. Then, impurity ions(antimony for nMOS and boron for pMOS) are implanted into the finstructure 112 to form the raised extension region 141 in the finstructure 112. Then, the impurities are activated by RTA (FIG. 4G).

Next, as in FIG. 2H, a Si oxide film 115C which is to be side wallinsulating films 115 (second side wall insulating films) is deposited byCVD, and gate side wall processing is performed by RIE. Then, impurityions (antimony for nMOS and boron for PMOS) are implanted intosource/drain regions 131 and a poly Si layer 114 (gate electrode 114)(FIG. 4H).

Next, as in FIG. 2I, the upper sides of the source/drain regions 131 andthe entire poly Si layer 114 (gate electrode 114) are Ni-silicided.Then, the gate structure is covered with an interlayer insulating film221. Then, contact holes are formed in the interlayer insulating film221. Then, source/drain electrodes 116 are formed in the contact holes.Thereby, the field effect transistor 101 shown in FIG. 3 is completed(FIG. 4I).

Third Embodiment

FIG. 5 is an explanatory view showing a field effect transistor 101 ofthe third embodiment.

In the third embodiment, an embedded oxide film 401, which is a specificexample of an embedded insulating film, is formed in the region wherethe under channel region 122 is formed in the second embodiment, and thechannel region 121 is formed above the embedded oxide film 401.Therefore, the embedded oxide film 401 is embedded under the channelregion 121 in the fin structure 112. In the third embodiment, since theembedded oxide film 401 is thus embedded under the channel region 121,the short channel effect can be further suppressed compared to the firstand second embodiments. Furthermore, the leak current from the extensionjunction can be reduced. As shown in the side cross-sectional view ofthe Y cross section, the gate insulating film 113 and the gate electrode114 partially intrude under the channel region 121, which alsocontributes to the suppression of the short channel effect. Since theother structural features are similar to those of the second embodiment,description thereof will be omitted.

FIGS. 6A to 6G are explanatory views showing a method for manufacturingthe field effect transistor 101 of the third embodiment.

Firstly, a strained Si_(0.4)Ge_(0.6) layer 112X having a thickness of 15nm, a strained Si_(0.85)Ge_(0.15) layer 112A having a thickness of 110nm, and a Si cap layer 112B having a thickness of 10 nm, are formed byepitaxial deposition as layers forming a fin structure 112. The SiGelayer 112X is formed on a Si substrate 111, the SiGe layer 112A isformed on the SiGe layer 112X, and the Si cap layer 112B is formed onthe SiGe layer 112A. Then, a Si thermal oxide film 201 having athickness of 4 nm is formed on the Si layer 112B by CVD, and a Sinitride film 202 is formed on the Si thermal oxide film 201 by CVD.Then, the Si nitride film 202 is patterned into a square shape byphotolithography, and then, the Si layer 112B, the SiGe layer 112A, theSiGe layer 112X, and the Si substrate 111 are etched to the depth of 150nm by RIE. Thereby, the fin structure 112 is formed on the Si substrate111 (FIG. 6A).

Then, as in FIG. 4A, a Si oxide film 301 is deposited over the entiresurface by CVD, and then, a Si nitride film 302 is deposited over theentire surface by CVD. Then, a window 311 is formed in the Si oxide film301 and the Si nitride film 302 by photolithography and RIE (FIG. 6B).

Next, the SiGe layer 112X exposed in the window 311 is removedselectively (i.e. etched selectively) by wet etching with fluoro-nitricacid or CDE, to form a cavity 411 in the fin structure 112 (FIG. 6C).

Next, as in FIG. 4B, thermal oxidization of the fin structure 112 isperformed. In this embodiment, a mask covers the area around the regionwhere the channel region 121 is to be formed, so generally, by thethermal oxidization, the Ge composition ratio in the channel region 121is increased, while the Ge composition ratio in the area around thechannel region 121 is not increased (FIG. 6D). During the thermaloxidization, the temperature of the thermal oxidization is decreasedstepwise or continuously from a high temperature to a low temperature,for example, from 1150° C. to 870° C., according to the increase of Gecomposition ratio. By such temperature adjustment, the interdiffusion ofthe Si and Ge atoms is accelerated, and hence the channel side regions123 having composition gradient of 5%/nm or lower are formed at sides ofthe channel region 121. Thereby, the occurrence of lattice defects inthe channel region 121, channel side regions 123, and the like, can besuppressed.

Next, as in FIG. 4C, the Si oxide film 301 and the Si nitride film 302are removed by hot phosphoric acid wet etching. Then, a Si oxide film203 is deposited by CVD, so that the region around the fin structure 112is filled with the Si oxide film 203. Thereby, a oxide film 401 (a partof the Si oxide film 203) is embedded in the cavity 411, i.e., thecavity 411 is filled with an embedded oxide film 401. Then, the Si oxidefilm 203 is planarized by CMP until the surface of the Si nitride film202 is exposed. Then, channel impurity ions and punch-through stopperimpurity ions (boron for nMOS and arsenic for pMOS) are implanted intothe channel region 121, under source/drain regions 132, and the like(FIG. 6E).

Next, as in FIG. 4D, the Si oxide film 203 is etched to the depth of 100nm by RIE using the Si nitride film 202 as a mask. Then, the Si nitridefilm 202, and the residual Si oxide film 203 on the sides of the finstructure 112, are removed by wet etching with hot phosphoric acid andwet etching with diluted hydrofluoric acid. Thereby, a plurality ofchannel surfaces of the channel region 121 are exposed above thesubstrate (FIG. 6F).

Next, as in FIG. 4E, a HfSiON film 113 which is to be a gate insulatingfilm 113, is deposited by CVD Then, a poly Si layer 114 which is to be agate electrode 114, is deposited. Then, as in FIG. 4F, gate processingis performed by photolithography and RIE. Then, a Si oxide film 115A anda Si nitride film 115B which is to be side wall insulating films 115(first side wall insulating films) are deposited, and gate side wallprocessing is performed by RIE (FIG. 6G).

Then, processes similar to those shown in FIGS. 4G, 4H, and 4I areperformed. Thereby, the field effect transistor 101 shown in FIG. 5 iscompleted.

Fourth Embodiment

FIG. 7 is an explanatory view showing a field effect transistor 101 ofthe fourth embodiment.

The fin structure 112 of the fourth embodiment is almost similar to thefin structure 112 of the third embodiment. One of the differencesbetween the fourth embodiment and the third embodiment is the shape ofthe fin structure 112. The fin structure 112 of the fourth embodimenthas a shape that the fin structure 112 is trimmed at the sides of thechannel region 121. Furthermore, in the fourth embodiment, Ni silicidefilms 421 are formed at the sides of the channel region 121. Since theNi silicide films 421 are in contact with the channel region 121,carriers are directly supplied from the Ni silicide films 421 to thechannel region 121. At the sides of the channel region 121, highconcentration impurity regions 431, which are very thin (5 nm or thinnerin this embodiment), are formed between the channel region 121 and theNi silicide films 421. By such a structure, parasitic resistance isreduced compared to the third embodiment which has diffusion layerextensions, so that a high drive current is obtained in the fourthembodiment. Furthermore, in the fourth embodiment, diffusion layersource and drain 131 are formed under the Ni silicide films 421, so thatpn junctions are formed between the substrate and the Ni silicide films421. The Ni silicide films 421 are a specific example of silicide films,and the high concentration impurity regions 431 are a specific exampleof impurity regions.

FIG. 8 is an explanatory view showing a method for manufacturing thefield effect transistor 101 of the fourth embodiment.

The field effect transistor 101 of the fourth embodiment can bemanufactured, by increasing the amount of overetching when the side walletching is performed in the process shown in FIG. 6G of the thirdembodiment. This results in providing the fin structure 112 shown inFIG. 8, i.e., the fin structure 112 having a shape that the finstructure 112 is trimmed at the regions 441 where the Ni silicide films421 are to be formed. Then, the high concentration impurity regions 431,and the semiconductor layers 421 which are to be the Ni silicide films421, are formed at the sides of the channel region 121. Thesemiconductor layers 421 are formed in the regions 441 where the Nisilicide films 421 are to be formed. Then, processes similar to thoseshown in FIGS. 4G, 4H, and 4I are performed. In the process shown inFIG. 4I, the semiconductor layers 421 are Ni-silicided. In thisembodiment, the process of forming the second side wall insulating films(FIG. 4G) is not required. By the processes described above, the fieldeffect transistor 101 shown in FIG. 7 is completed.

Fifth Embodiment

FIG. 9 is an explanatory view showing a field effect transistor 101 ofthe fifth embodiment.

While the FET 101 of the third embodiment employs the tri-gatestructure, the FET 101 of the fifth embodiment employs thegate-all-around (GAA) structure. Therefore, in the FET 101 of the fifthembodiment, the channel region 121 is surrounded tubularly by the gateinsulating film 113 and the gate electrode 114. In the FET 101 of thefifth embodiment, by employing the GAA structure, not only the effect ofthe FET 101 of the third embodiment is achieved, but also the shortchannel effect is more suppressed. In this embodiment, the gateelectrode 114 is a laminated film (three-layer film) formed of a TiNfilm 114A, a poly Si film 114B, and a Ni silicide film 114C, andsurrounds the channel region 121 via the gate insulating film 113.

As shown in the side cross-sectional view of the Y cross section, thechannel surfaces of the channel region 121 of this embodiment areconstituted by a first lateral channel surface S1, a second lateralchannel surface S2, an upper channel surface S3, and a lower channelsurface S4, and these channel surfaces form a tubular shape having arectangular cross section. The gate insulating film 113 of thisembodiment is formed on the tubular channel surface formed of thechannel surfaces S1, S2, S3, and S4. The gate electrode 114 (114A and114B) of this embodiment is formed on the insulating film 113 on thetubular channel surface formed of the channel surfaces S1, S2, S3, andS4.

FIG. 10 is an explanatory view showing a method for manufacturing thefield effect transistor 101 of the fifth embodiment.

The field effect transistor 101 of the fifth embodiment can bemanufactured, by continuing the wet etching of the Si oxide film 203 inthe process shown in FIG. 6F of the third embodiment, until a part(upper part) of the embedded oxide film 401 is removed as shown in FIG.10. Thereby, a cavity 501 in the fin structure 112 is formed under thechannel region 121. By forming the gate insulating film 113 and the gateelectrode 114 (114A and 114B) under the condition that the cavity 501 isopen in the fin structure 112 as shown in FIG. 10, the GAA structureshown in FIG. 9 can be formed. Then, processes similar to those shown inFIGS. 6G, 4G, 4H, and 4I are performed. The gate electrodes 114A and114B are formed before the cavity 501 is blocked, and the gate electrode114C is formed after the cavity 501 is blocked. By the processesdescribed above, the field effect transistor 101 shown in FIG. 9 iscompleted.

Sixth Embodiment

FIG. 11 is an explanatory view showing a field effect transistor 101 ofthe sixth embodiment.

In the fifth embodiment, one channel region 121 is formed in one finstructure 112, so that one GM structure is formed in one fin structure112. On the other hand, in the sixth embodiment, three channel regions121 a, 121 b, and 121 c are formed in one fin structure 112, so thatthree GAA structures are formed in one fin structure 112. Therefore, inthe sixth embodiment, one fin structure 112 has a plurality ofstructures in each of which one of a plurality of the channel regions121 is surrounded tubularly by the gate insulating film 113 and the gateelectrode 114. Thus, in the sixth embodiment, a drive current aboutthree times higher than that in the fifth embodiment is obtained. It isnot necessary that the number of the channel regions 121 in one finstructure 112 be limited to three. If the number of the channel regions121 is N, the drive current becomes about N times higher than that inthe fifth embodiment.

In this embodiment, as shown in the side cross-sectional view of the Ycross section, three GAA structures such as, the structure thatsurrounds the channel region 121 a, the structure that surrounds thechannel region 121 b, and the structure that surrounds the channelregion 121 c, are formed at three locations such as, the area around thechannel region 121 a, the area around the channel region 121 b, and thearea around the channel region 121 c. Each of the channel surfaces Sa,Sb, and Sc of the channel regions 121 a, 121 b, and 121 c, forms atubular shape. The gate insulating film 113 of this embodiment is formedon the tubular channel surfaces Sa, Sb, and Sc. The gate electrode 114(114A and 114B) of this embodiment is formed on the gate insulating film113 on the tubular channel surfaces Sa, Sb, and Sc. Each of the channelregions 121 a, 121 b, and 121 c has a thin stick-like shape. Compositionof each of the channel regions 121 a, 121 b, and 121 c is similar to thechannel region 121 in the first to fifth embodiments. In thisembodiment, each of the channel regions 121 a, 121 b, and 121 c is Geregion.

FIGS. 12A to 12C are explanatory views showing a method formanufacturing the field effect transistor 101 of the sixth embodiment.

Firstly, a Si_(0.4)Ge_(0.6) layer 112X, a plurality ofSi_(0.85)Ge_(0.15) layers 112Aab and 112Abc, and a plurality of Silayers 112Ba, 112Bb and 112Bc, are formed over a Si substrate 111 byepitaxial deposition as layers forming a fin structure 112. The order oflamination is, from the bottom layer, (the Si substrate 111,) the SiGelayer 112X, the Si layer 112Ba, the SiGe layer 112Aab, the Si layer112Bb, the SiGe layer 112Abc, and the Si layer 112Bc. Then, processessimilar to those shown in FIGS. 6A, 6B, and 6C are performed. Thereby,the structure having the fin structure 112 on the Si substrate 111 shownin FIG. 12A is fabricated.

Next, as in FIG. 6D, thermal oxidization of the fin structure 112 isperformed. Thereby, a plurality of channel regions 121 a, 121 b, and 121c shown in FIG. 12B are formed. This is because, the oxidization speedof SiGe is faster than that of Si, and hence the Si_(0.85)Ge_(0.15)portions of the side walls of the fin structure 112 are recessedrelative to the other portions as the thermal oxidization in the finstructure 112 proceeds, so that when the thermal oxidization in the finstructure 112 sufficiently proceeds, the recessed portions are connectedto each other, and then a channel region 121 is divided. In such anoxidization process, the interface between SiGe and Si present beforeoxidization, is eliminated by the interdiffusion of the Si and Ge atoms,and the Ge composition becomes uniform as the oxidization proceeds. Geis condensed in the regions which are left because of uneven structureson both sides, and Si_(1-x)Ge_(x) (x≧0.8) channels are formed in part ofthe regions which have initially been the Si layers. Alternatively, ifuneven structures are formed before the thermal oxidization by selectiveetching with fluoric-nitric acid or the like on the side walls of thefin structure 112, such that the SiGe layers 112Aab and 112Abc arerecessed relative to the Si layers 112Ba, 112Bb and 112Bc, as shown inFIG. 12C, there is provided an advantage that the degree of designfreedom of the channel size and the channel interval is increased. Thisis because, while the height of the uneven structures is determineduniquely, in the structure shown in FIG. 12A, by the difference in theoxidization speeds, the height of the uneven structures can be setarbitrarily, in the structure shown in FIG. 12C, in a certain range byadjusting the time of the selective etching.

Then, processes similar to those shown in FIGS. 6E to 6G and FIGS. 4G to4I are performed as in the fifth embodiment. In the process shown inFIG. 6F, the wet etching of the Si oxide film 203 is continued until apart (upper part) of the embedded oxide film 401 is removed, as in thefifth embodiment. Thereby, the cavities 501 in the fin structure 112 areformed, under the channel region 121 a, between the channel region 121 aand the channel region 121 b, and between the channel region 121 b andthe channel region 121 c. By forming the gate insulating film 113 andthe gate electrode 114 (114A and 114B) under the condition that theplurality of cavities 501 are open in the fin structure 112, theplurality of GAA structures can be formed. By the processes describedabove, the field effect transistor 101 shown in FIG. 11 is thuscompleted.

In the first to sixth embodiments, various variations are conceivablefor the gate insulating film 113, the gate electrode 114, and thesource/drain regions 131. Examples of employable materials to form thegate insulating film 113 are HfSiO₂, HfO₂, HfArO_(x) and ZrO₂, which arehigh permittivity materials other than HfSiON. Alternatively, the gateinsulating film 113 may be a laminated film formed of an insulating filmmade of any of these high dielectric constant materials and aninsulating film made of SiO₂ or GeO₂. Alternatively, a SiON film or aSiO₂ film may also be employed as the gate insulating film 113. Further,as the gate electrode 114, Ni germanoid (Ni_(1-x)Ge_(x)), Nigermano-silicide (NiSi(Ge)), W (tungsten) silicide, TiSiN, TaN, TaSiN,WN, AlN, or the like may be employed.

In the first to sixth embodiments, although the Ge channel orSi_(1-x)Ge_(x) (x≧0.8) channel is used for both of the nMOS and pMOSwhich are components of the CMOS, a Si channel may be used for the nMOS.In this case, for example, the SiGe layer 112A and the Si layer 112B maybe formed by, forming a selective deposition mask formed of a Si oxidefilm or a Si nitride film in the nMOS region in advance, then,depositing selectively the SiGe layer 112A and the Si layer 112B in thepMOS region, and then, removing the selective deposition mask. Inaddition, after the removal of the selective deposition mask, anotherselective deposition mask may be formed in the pMOS region and furtherSi may be laminated in the nMOS region by selective epitaxialdeposition, to eliminate the step between the nMOS region and the pMOSregion. In this case, the Ge composition ratio in the pMOS channelregion 121 may be lower than 80%; the Ge composition ratio in the pMOSchannel region 121 lower than 80% is desirable. This is because, whenthe Ge composition ratio in SiGe decreases, the melting point of SiGeincreases, and hence the melting point of SiGe approaches the meltingpoint of Si, so that the process temperature of SiGe-pMOS can be easilyapproached the process temperature of Si-nMOS. The contents of thisparagraph will also be described in the following seventh embodiment.

Seventh Embodiment

FIG. 13 is an explanatory view showing a field effect transistor 101 ofthe seventh embodiment.

The FET 101 shown in FIG. 13 is an example in which an SOI(Semiconductor-On-Insulator) substrate 601 is used as the substrateinstead of the bulk Si substrate 111. The FET 101 shown in FIG. 13employs a structure in which the embedded oxide film 401 under thechannel in the third embodiment is replaced with an embedded oxide film611 that forms the SOI substrate 601. Therefore, the embedded oxide film611, which is a specific example of an embedded insulating film, is alsopresent under the source and drain. This embodiment has a disadvantagethat the cost of the substrate is increased compared to the thirdembodiment, but has advantages that, not only the effect of the thirdembodiment is achieved, but also the off-state current can be reducedsince the source/drain regions 131 are well-insulated from the substrate601. Furthermore, with regard to the manufacturing process thereof, thisembodiment has an advantage that the processes of etching back theinterlayer film and exposing the fin as shown in FIG. 6F are notrequired, which simplifies the manufacturing process.

Eighth Embodiment

FIG. 14 is an explanatory view showing a field effect transistor 101 ofthe eighth embodiment.

The FET 101 shown in FIG. 14 includes a Si substrate 111, a first finstructure 112M, a second fin structure 112N, a gate insulating film 113,and a gate electrode 114.

The first fin structure 112M and the second fin structure 112N areformed on the common Si substrate 111. Each of the first fin structure112M and the second fin structure 112N corresponds to any one of the finstructures of the first to sixth embodiments. A first channel region121M, which is a Ge region or a SiGe region, is formed in the first finstructure 112M, and a second channel region 121N, which is a Ge regionor a SiGe region, is formed in the second fin structure 112N. The commonsource/drain regions 131 are formed at the sides of the first channelregion 121M and the second channel region 121N. The gate insulating film113 is formed on the first channel region 121M and the second channelregion 121N (particularly in this embodiment, on the surface across aplurality of channel surfaces of the first channel region 121M and aplurality of channel surfaces of the second channel region 121N). Thegate electrode 114 is formed on the gate insulating film 113 on thefirst channel region 121M and the second channel region 121N(particularly in this embodiment, on the surface across a plurality ofchannel surfaces of the first channel region 121M and a plurality ofchannel surfaces of the second channel region 121N).

In the FET 101 shown in FIG. 14, since the first channel region 121M andthe second channel region 121N are connected to the common source/drainregions 131, the FET 101 shown in FIG. 14 can be handled as a singletransistor. In the FET 101 shown in FIG. 14, since the effective channelwidth is twice the channel width of the FET 101 shown in FIG. 1 and thelike, a drain current two times higher than that in the FET 101 shown inFIG. 1 and the like, is obtained.

The FET 101 shown in FIG. 14 may include three or more fin structures112 each of which corresponds to any one of the fin structures of thefirst to sixth embodiments. Furthermore, the FET 101 shown in FIG. 14may include also one or more fin structures 112 each of whichcorresponds to none of the fin structures of the first to sixthembodiments.

The FET 101 shown in FIG. 14 can be manufactured by using any one of themanufacturing methods of the first to sixth embodiments. However, thegate insulating film 113, the gate electrode 114, and the source/drainregions 131 need to be common to the first channel region 121M and thesecond channel region 121N.

Ninth Embodiment

FIG. 15 is an explanatory view showing (main components of) a CMOScircuit 701 of the ninth embodiment.

The CMOS circuit 701 shown in FIG. 15 is constituted by a pMOS 101 p andan nMOS 101 n. The pMOS 101 p is a SiGe-FinFET that corresponds to anyone of the FETs of the first to eighth embodiments, while the nMOS 101 nis a Si-FinFET that corresponds to none of the FETs of the first toeighth embodiments. The CMOS circuit 701 shown in FIG. 15 corresponds toa specific example of an integrated circuit element, i.e., acomplementary MIS (Metal-Insulator-Semiconductor) circuit element, ofthe present invention.

The pMOS 101 p and the nMOS 101 n are formed on the common Si substrate111. A fin structure 112 p which forms the pMOS 101 p, and a finstructure 112 n which forms the nMOS 101 n, are formed on the Sisubstrate 111. The fin structure 112 p is a SiGe-Fin that corresponds toany one of the fin structures of the first to eighth embodiments, whilethe fin structure 112 n is a Si-Fin that corresponds to none of the finstructures of the first to eighth embodiments.

A channel region 121 p, which is a Si_(0.6)Ge_(0.4) region, is formed inthe fin structure 112 p. A gate insulating film 113 p is formed on aplurality of the channel surfaces of the channel region 121 p. A gateelectrode 114 p is formed on the gate insulating film 113 p on aplurality of the channel surfaces of the channel region 121 p. A channelregion 112 n, which is a Si region, is formed in the fin structure 112n. A gate insulating film 113 n is formed on a plurality of the channelsurfaces of the channel region 121 n. A gate electrode 114 n is formedon the gate insulating film 113 n on a plurality of the channel surfacesof the channel region 121 n.

In the ninth embodiment, not only the pMOS 10 p, but also the nMOS 101n, can be manufactured by using any one of the manufacturing methods ofthe first to eighth embodiments. However, a Si-Fin instead of a SiGe-Finis formed, as the fin structure 112 n of the nMOS 101 n. When the finstructures 112 p and 112 n are formed, the things described in the lastparagraph in the sixth embodiment are to be taken into account. Withregard to the Si-Fin of the nMOS 101 n and the SiGe-FinFET of the pMOS101 p, the Si-Fin corresponds to the SiGe-FinFET whose Ge atoms arereplaced with Si atoms.

In the first to ninth embodiments, the combination of the surfaceorientation of the substrate and the channel direction of the transistoris arbitrarily configured. Specific examples of representativecombinations include, the [110]-direction channel combined with thesubstrate having a principal plane (001), the [100]-direction channelcombined with the substrate having a principal plane (001), the[100]-direction channel combined with the substrate having a principalplane (011), and the [01-1]-direction channel combined with thesubstrate having a principal plane (011). Further, an SOI substrate canbe used as the substrate in the embodiments other than the seventhembodiment. In this case, as in the seventh embodiment, there is adisadvantage in terms of the substrate cost, but there are advantages interms of the reduced off-state current and the simplified manufacturingprocess.

As described above, the embodiments of the present invention providesnovel field effect transistor and manufacturing method thereof, withregard to a field effect transistor having a multi-gate structureprovided with a channel region containing Ge atoms, and a manufacturingmethod thereof.

1. A field effect transistor comprising: a semiconductor substratecontaining Si atoms; a protruding structure formed on the semiconductorsubstrate; a channel region formed in the protruding structure andcontaining Ge atoms; an under channel region formed under the channelregion in the protruding structure and containing Si and Ge atoms, theGe composition ratio among Si and Ge atoms contained in the underchannel region continuously changing from the channel region side to thesemiconductor substrate side; a gate insulating film formed on thechannel region; and a gate electrode formed on the gate insulating filmon the channel region.
 2. The field effect transistor according to claim1, further comprising: source/drain regions formed at sides of thechannel region and containing Si and Ge atoms, the Ge composition ratioamong Si and Ge atoms contained in the source/drain regions being lowerthan the Ge composition ratio in the channel region; and channel sideregions formed between the channel region and the source/drain regionsat sides of the channel region and containing Si and Ge atoms, the Gecomposition ratio among Si and Ge atoms contained in the channel sideregions continuously changing from the channel region sides to thesource/drain region sides.
 3. The field effect transistor according toclaim 1, wherein the Ge composition ratio in the channel region is 80%or higher.
 4. The field effect transistor according to claim 1, whereinthe thickness of the under channel region from the channel region sideto the semiconductor substrate side is 250 nm or smaller.
 5. The fieldeffect transistor according to claim 1, wherein the rate of change ofthe Ge composition ratio from the channel region side to thesemiconductor substrate side in the under channel region is 5%/nm orlower.
 6. A field effect transistor comprising: a semiconductorsubstrate containing Si atoms; a protruding structure formed on thesemiconductor substrate; a channel region formed in the protrudingstructure and containing Ge atoms; an insulating film embedded under thechannel region; a gate insulating film formed on the channel region; anda gate electrode formed on the gate insulating film on the channelregion.
 7. The field effect transistor according to claim 6, furthercomprising: source/drain regions formed at sides of the channel regionand containing Si and Ge atoms, the Ge composition ratio among Si and Geatoms contained in the source/drain regions being lower than the Gecomposition ratio in the channel region; and channel side regions formedbetween the channel region and the source/drain regions at sides of thechannel region and containing Si and Ge atoms, the Ge composition ratioamong Si and Ge atoms contained in the channel side regions continuouslychanging from the channel region sides to the source/drain region sides.8. The field effect transistor according to claim 6, further comprising:silicide films formed at sides of the channel region; source/drainregions formed under the silicide films; and impurity regions formedbetween the channel region and the silicide films at sides of thechannel region.
 9. The field effect transistor according to claim 6,wherein the protruding structure has a structure in which the channelregion is surrounded tubularly by the gate insulating film and the gateelectrode.
 10. The field effect transistor according to claim 9, whereina plurality of channel regions are formed in the protruding structure,and the protruding structure has a plurality of structures in each ofwhich one of the plurality of channel regions is surrounded tubularly bythe gate insulating film and the gate electrode.
 11. The field effecttransistor according to claim 1 or 6, further comprising: anotherprotruding structure formed on the semiconductor substrate; and anotherchannel region formed in the another protruding structure and containingGe atoms; wherein the gate insulating film is formed on the channelregion and the another channel region, and the gate electrode is formedon the gate insulating film on the channel region and the anotherchannel region.
 12. An integrated circuit element which is acomplementary MIS (Metal-Insulator-Semiconductor) circuit elementcomprising a P-type field effect transistor and an N-type field effecttransistor, wherein the P-type field effect transistor is a field effecttransistor according to claim 1 or 6, and the N-type field effecttransistor is a field effect transistor according to claim 1 or 6 inwhich Ge atoms in the channel region are replaced with Si atoms.
 13. Amethod for manufacturing a field effect transistor, the methodcomprising: forming a protruding structure on a semiconductor substratecontaining Si atoms; by thermal oxidization, forming a channel regioncontaining Ge atoms in the protruding structure; by changing thetemperature of the thermal oxidization from a high temperature to a lowtemperature, forming an under channel region containing Si and Ge atomsunder the channel region in the protruding structure, the Ge compositionratio among Si and Ge atoms contained in the under channel regioncontinuously changing from the channel region side to the semiconductorsubstrate side; forming a gate insulating film on the channel region;and forming a gate electrode on the gate insulating film on the channelregion.
 14. A method for manufacturing a field effect transistor, themethod comprising: forming a protruding structure on a semiconductorsubstrate containing Si atoms; by thermal oxidization under thecondition that a mask covers the area around the region where a channelregion is to be formed, forming a channel region containing Ge atoms inthe protruding structure; by changing the temperature of the thermaloxidization from a high temperature to a low temperature, forming anunder channel region containing Si and Ge atoms under the channel regionin the protruding structure, the Ge composition ratio among Si and Geatoms contained in the under channel region continuously changing fromthe channel region side to the semiconductor substrate side, and formingchannel side regions containing Si and Ge atoms at sides of the channelregion, the Ge composition ratio among Si and Ge atoms contained in thechannel side regions continuously changing from the channel region sidesto source/drain region sides; forming source/drain regions containing Siand Ge atoms at sides of the channel region, the Ge composition ratioamong Si and Ge atoms contained in the source/drain regions being lowerthan the Ge composition ratio in the channel region; forming a gateinsulating film on the channel region; and forming a gate electrode onthe gate insulating film on the channel region.
 15. A method formanufacturing a field effect transistor, the method comprising: forminga protruding structure on a semiconductor substrate containing Si atoms;forming a cavity in the protruding structure; embedding an insulatingfilm in the cavity; by thermal oxidization, forming a channel regioncontaining Ge atoms in the protruding structure; forming a gateinsulating film on the channel region; and forming a gate electrode onthe gate insulating film on the channel region.
 16. The method accordingto claim 15, further comprising: forming impurity regions at sides ofthe channel region; forming silicide films at sides of the channelregion; and forming source/drain regions under the silicide films. 17.The method according to claim 15, by forming the gate insulating filmand the gate electrode under the condition that a cavity is open in thefin structure, forming the protruding structure having a structure inwhich the channel region is surrounded tubularly by the gate insulatingfilm and the gate electrode.
 18. The method according to claim 17, byforming a plurality of channel regions in the protruding structure andforming the gate insulating film and the gate electrode under thecondition that a plurality of cavities are open in the fin structure,forming the protruding structure having a plurality of structures ineach of which one of the plurality of channel regions is surroundedtubularly by the gate insulating film and the gate electrode.
 19. Themethod according to any one of claims 13 to 15, further comprising:forming another protruding structure on the semiconductor substrate; andforming another channel region containing Ge atoms in the anotherprotruding structure; wherein the gate insulating film is formed on thechannel region and the another channel region, and the gate electrode isformed on the gate insulating film on the channel region and the anotherchannel region.
 20. A method for manufacturing an integrated circuitelement which is a complementary MIS (Metal-Insulator-Semiconductor)circuit element comprising a P-type field effect transistor and anN-type field effect transistor, the method comprising: forming, as theP-type field effect transistor, a field effect transistor according toclaim 1 or 6; and forming, as the N-type field effect transistor, afield effect transistor according to claim 1 or 6 in which Ge atoms inthe channel region are replaced with Si atoms.